Numerous situations require close monitoring of static charge buildup on objects, including personnel, such as in the manufacture and testing of voltage sensitive electronic components and equipment, so that steps can be taken to establish a "static-free" electronic workshop. Manufacturing operations that involve continuous movements of web, sheet, particulate, and powder materials invariably pickup hazardous static charges, which must be safety dissipated. Thus, it is important to measure and monitor the static charges on these materials, so that appropriate grounding provisions can be implemented. Measurement of electrostatic charge is also necessary in the testing of ionizers and electrostatic precipitators.
All of these situations require that measurement of static charge buildup be conducted without contacting the material, otherwise the consequent charge dissipation will result in inaccurate voltage measurements and possible violent static discharge hazardous to personnel and equipment.
Non-contact fieldmeters or voltmeters are known in the art, such as exemplified by commonly assigned U.S. Pat. No. 4,853,639, the disclosure of which is incorporated herein by reference. Such prior art fieldmeters may be in the form of a handheld, battery-powered instrument that includes a probe or electrode, which is positioned to in the electrostatic field produced by a charged object and thus may be capacitively coupled with the charged object. The voltage produced on the probe, which is indicative of the electrostatic voltage on the object surface, is processed to generate a readout of the electrostatic voltage on, for example, a meter scale or an LCD display. Since the magnitude of the probe voltage is a function of its position in the electrical field, accurate voltage readings require that the probe be placed in predetermined spaced relation to the charged object.
Other important considerations for voltage reading accuracy include zero adjustment of the fieldmeter, which is frequently required Heretofore, fieldmeters have typically been equipped with a user adjustable potentiometer included in the electronic signal processing circuitry. To zero the voltage readout, the user positions the probe away from any charged objects and turns, for example, a thumbwheel linked to the zero-adjust potentiometer until a zero voltage readout is obtained. While this manual zero adjustment procedure is generally effective, it is nevertheless inconvenient and time consuming.